Such drip emitters are normally coupled to an irrigation pipe and are provided with an inlet, an outlet and a flow-restricting path therebetween. Liquid passing from the pipe via the inlet into the emitter; traverses through the flow-restricting path to be released at the outlet of the emitter at a relatively low discharge pressure generally equal to about zero.
U.S. Pat. No. 6,250,571, the disclosure of which is incorporated herein by reference, describes a drip irrigation emitter having a non-regulating labyrinth that functions to reduce pressure of water entering the emitter before it reaches a regulating labyrinth. A modification of the emitter has an opening that serves as an outlet from the non-regulating labyrinth and an inlet to the regulating labyrinth. This opening is covered by a membrane that functions as a one-way valve permitting flow of water only from the non-regulating labyrinth to the regulating labyrinth.
U.S. Pat. No. 5,111,996, the disclosure of which is incorporated herein by reference, describes an emitter having valves that are used to control the length of a fluid flow limiting passageway. The passageway is divided into sections and as the pressure in the pipe increases beyond predetermined values, valves that are located along the passageway close to force fluid to flow through additional sections of the passageway.